Sundials - World's Oldest Clocks

North American Sundial Society

Transits Time and Longitude

Here we showcase various natural and scientific phenomena related to the sun and solar alignments, and the quest for measuring time and longitude.

The North American Sundial Society will meet in St. Louis for their annual meeting and to observe the Great American Solar Eclipse on August 21, 2017.  Cities and towns across the US are planning events and raising awareness of both the beauty and hazards of the solar eclipse. For the last two years St. Louis groups have delivered more than 100 programs to area schools, libraries, cities, parks and businesses to raise awareness of this historic event which has not happened in St. Louis since the year 1442. 

Remember, except for the minute or two of totality, looking directly at the sun will do serious eye damage.  Use sun-safe eyeglasses (certified safe for solar viewing) available from many source (see links below or Amazon, etc.). Read about the Great American Eclipse coming near you:

St. Louis, IL:

Other Cities:

The 2017 August 21st solar eclipse will be commemorated by the US Postal Service with a unique thermochromic ink Forever Stamps: the stamp shows the total Eclipse of the Sun with its corona blocked by a black disk of the moon.  However, using the body heat of your thumb or fingers the eclipse image will reveal an underlying image of the moon. The image reverts back to the eclipse once it cools. Fred Espenak, "Mr. Eclipse" a retired NASA astrophysicist, took the photograph of both the eclipse (from Jalu, Libya on March 29, 2006) and the full moon.

The USPS  states that June 20, 1:30 p.m. MT will be theFirst-Day-of-Issue ceremony, taking place at the Art Museum of the University of Wyoming (UW) in Laramie. The University is celebrating the summer solstice on June 20. Prior to the stamp issuance, visitors are encouraged to arrive at UW's Art Museum's Rotunda at 11:30 a.m. to witness a unique architectural feature at noon when a single beam of sunlight shines from down on a silver dollar embedded in the floor, marking noon on the summer solstice,

The Total Eclipse of the Sun Forever Stamps may be pre-ordered at in early June for delivery following the June 20 nationwide issuance.  The back of the stamp pane provides a map of the eclipse path and times it appears at cities across the US.

Back Panel of the Eclipse Stamp

Read more at: NASA Eclipse    and for observing tips

At the Grolier Club on the Upper East Side of Manhattan is a massive exhibit  On Time: The Quest for Precision curated by Bruce Bradley.  The exhibit presents the progress of timekeeping over six centuries through 86 rare books from the Linda Hall Library of Science, Engineering & Technology.

La pratique et demonstration des horloges solaires
1624 La pratique et demonstration des horloges solaires

Journalist Allison Meier of describes a number of books on display such as "German cartographer Sebastian Münster’s 1533 Horologiographia, the first book devoted to sundials, with woodcuts attributed to Hans Holbein the Younger."  As shown in her photo, "French engineer Salomon de Caus’s 1624  La pratique et demonstration des horloges solaires has embedded pop-ups to make the workings of its sundials easier to replicate."

The scope of "On Time" stretches from sundials, to water clocks, mechanical clocks and even a Pilkington & Gibbs Heliochronometer, ending with our latest atomic clocks.  The display flirts with the possible.  While Benjamin Franklin may have suggested using hourly time-telling canon in the 18th century, Athanasius Kircher proposed a fanciful firing sundial a century earlier in his 1646 Ars magna lucis et umbrae in decem libros digesta. His bowl-shaped sundial holds gunpowder at the hours that is ignited by the rays of the sun from a lens.  In turn the firing gunpowder triggers hammers to toll hourly bells. If one thinks about this for a moment, Kircher's proposal is as unrealistic as Franklin's.  The change in solar declination creates problems for proper placement of the gunpowder, let alone directing the ignition to trigger hammers.

Allison observes that "These manuscripts affirm the centuries of shared ideas that give our modern timekeeping devices their precision."  On Time: The Quest for Precision" continues through November 19, 2016.

Read more at:

What do Omega Psi Phi fraternity of Howard University Washington DC, Merton College in Oxford, Nashotah House Theological Seminary in Wisconsin, and Lewis Carroll's poem Jabberwocky all have in common?  Dancing and ceremonies around a sundial!  In Carroll's poem of 1885 "the slithy toves did gyre and gimble in the wabe" and as Alice explains to Humpty Dumpty, “Toves are curious creatures that are something like badgers, something like lizards, and something like corkscrews. They make their nests under sun-dials and live on cheese." and “Wabe is the grass-plot round a sun-dial. It is called like that because it goes a long way before it, and a long way behind it. And a long way beyond it on each side."

At Howard University in the center of the main campus quadrangle is a bronze sundial on a 3-foot fluted limestone pedestal, gifted in 1929 to the university in honor of Benjamin Banneker, surveyor of the city of Washington DC, clockmaker, and sundialist. 

Read more: Sundials and Timely Ceremonies

With all due respects to Shakespeare, time will always be with us, and signifies quite a lot. The Harvard-Smithsonian Center for Astrophysics is organizing a symposium dedicated to Time and Culture to be held 5-9 June 2016 at Harvard's Northwest Lab.  According to the symposium organizers:

"The symposium aims to set the stage for future timekeeping standards, infrastructure, and engineering best practices for astronomers and the broader society. At the same time the program will be cognizant of the rich history from Harrison's chronometer to today's atomic clocks and pulsar observations. The theoreticians and engineers of time will be brought together with the educators and historians of science, enriching the understanding of time among both experts and the public."

The definition of the second has changed several times over the last 40 years and likely will change again before the end of this decade. Should timekeeping be decoupled from the rotation of the earth?  We already abstract time with zone time (such as Eastern Standard Time) and minipulate it to fit our activities (using Eastern Daylight Saving Time).  We no longer worry about the moment of sunrise or sunset, rather that we go to work at 9:00AM or have a class that lasts from 10:00-10:50AM.  Indeed, "ante and post meridian" may be obsolete.  

"The future of timekeeping is evolving with the development of optical frequency standars, the consideration of high-order relativistic effects, and the challenges of distributing trusted timescales at even higher preicision....A closer look at time in astronomy and other sciences, as a defining element of modern civilization, is needed."  Read more and register for the symposium at: